2007 5.3 Cast Iron with AFM. Around 50k miles. Average approximately 5000 between changes. Changed the oil around 40k miles, added one quart before the next change. The same thing happened after the next change. 1000 miles after my most recent change it needed a quart, added another quart today, after about a 1000 more miles. Information center says oil is currently at 55%. At this rate I'll use 3-4 quarts between changes, 10,000 miles ago it was zero. Taking it to the dealer as soon as I can.